Three-phase A.C. power sources are commonly used as power sources for a variety of commercial and household electrical systems. For example, a three-phase A.C. power source can be used as a power source for electric motors, air conditioners, boilers, electrical lightening systems etc.
A typical three-phase A.C. power source generates three alternating phase voltages of the same frequency. The three alternating phase voltages can be represented by sinusoidal waveforms of the same amplitudes, but with a phase difference of 120 degrees between each other. The three sinusoidal waveforms follow a definite sequence, which repeats itself periodically. This period is based on the frequency of the A.C. power source.
The phase difference between the sinusoidal waveforms is critical, since the correct phase difference between the waveforms indicates that the A.C. power source is functioning properly. However, it is possible that the phase difference between any two phase voltages of the three-phase A.C. power source deviates from its correct value, i.e., 120 degrees. The deviation from 120 degrees can occur due to phase loss or phase reversal in the AC power source. As a result, the A.C. power source may not function properly and may adversely affect the load connected to it. In such an event, the load may overheat and get damaged. To prevent damage to the load due to the improper functioning of the A.C. power source, many conventional techniques have been used to monitor the phase differences between each of the individual phase voltages of the A.C. power source.
One such conventional technique uses a three-phase detector to monitor the waveforms of each of the three phase voltages. The three-phase detector uses three opto-isolators to monitor waveforms. An opto-isolator is a device that transfers signals from its input to its output by using an optical path. Each of the three phase voltages is measured with reference to the earth/ground at different time intervals. Further, it is checked whether each of the phase voltages is high or low in a proper sequence and at proper times. An abnormality in the timings of the waveforms suggests that the A.C. power source is faulty. In such an event, the A.C. power source can be replaced or repaired.
However, the three-phase detector suffers from some limitations. Firstly, three separate opto-isolators are required to monitor each of the phase voltages. The use of three opto-isolators is not cost-effective. Secondly, the three-phase detector is not switched off when no phase detection is being carried out, which results in high power consumption. Therefore, there is a need for reducing the number of components in the three-phase detector. Further, there should be a provision for switching off the three-phase detector when the three-phase detection is complete.